Because of its attendant size, weight and cost, it has been occasionally found preferable to circumvent the use of an input line-isolation transformer in the design of television receivers. In such receivers, commonly referred to as "hot-chassis" receivers, the necessary voltage supplies are then directly derived from the AC line and returned to an AC or "Hot" ground. Typically, the AC line voltage is rectified and filtered to produce an unregulated output voltage of an amplitude necessarily dependent on the peak AC line voltage. In the receiver to be described below, this unregulated voltage is approximately 165 volts. The unregulated voltage may then be regulated or otherwise tailored to provide the necessary voltages for various portions of the receiver's circuitry. For example, as described below, the unregulated 165 volts is regulated to provide the 112-volt Horizontal B+ required by the horizontal output stage. Other parts of the receiver, for example, the tuner, video, sound and horizontal and vertical oscillator circuitry may require voltages in the range of 10 to 30 volts. In a conventional design the Horizontal B+ may be dropped simply through a dropping resistor or a series-pass transistor in order to develop the desired voltages. However, it is obvious to those skilled in the art that the voltage dropped, and hence power dissipated, across the resistor or series-pass transistor represents wasted energy to the extent that it serves no useful purpose in the operation of the receiver. In addition to wasting energy, this power dissipation results in the generation of sufficient heat in the receiver cabinet to cause thermal stress to other components as well as possible premature failure.
The subject invention represents a novel concept for supplying the lower voltages required by the receiver's circuitry while conserving energy to substantially the maximum extent possible. The essence of the concept is to provide additional secondary windings on the flyback transformer so as to develop these voltages. The alternating current developed by the horizontal output transistor in the flyback primary induces voltages in these secondary windings that can be rectified and filtered to effect the desired voltages.
Obviously, in order for the circuitry that is powered from the flyback secondary windings to be operational, there must be a signal developed in the flyback primary; that is, the horizontal oscillator must be operating. Consequently, the power supply for the oscillator cannot be solely dependent on the voltage induced in a flyback secondary winding. As before, the Horizontal B+ can be conveniently used to power the oscillator. However, since the Horizontal B+ is typically on the order of 100 V. and the voltage required by the oscillator may be approximately 20 V., the Horizontal B+must be dropped through, for example, a dropping resistor or series-pass transistor. In so doing a significant amount of power will necessarily be dissipated across the resistor or transistor. A considerably more desirable configuration would allow the oscillator also to be powered from a flyback secondary winding of an appropriate voltage.